GENERATING action and expressed MATHEMATICALLY as\({E_b} = \frac{{ZP\phi N}}{A}\)Eb = V – Ia RaWhere,Z = number of conductorsP = number of polesϕ = Magnetic flux in weberN = speed of the motor in rpmA = number of parallel pathV = TERMINAL voltageIa = Armature currentRa = Armature resistanceWhen the armature winding of a dc motor starts rotating in the magnetic flux produced by the field winding, it cuts the lines of magnetic flux.Hence according to Faraday's laws of electromagnetic induction, there will be an induced emf in the armature winding.As per Lenz’s law, this induced emf acts in the opposite direction to the armature VOLTAGE. Hence the emf is called as the back emf and is denoted by Eb.The back emf is proportional to the speed ‘N’. It is zero at standstill.Back emf opposes the supply voltage and LIMITS the armature current to a safe value.The supply voltage induces the current in the coil which rotates the armature. The electrical work required by the motor for causing the current against the back emf is converted into mechanical energy.So that energy is induced in the armature of the motor. Thus, the energy conversion in DC motor is possible only because of the back emf.